There is no such a thing as casual Christianity. Now, there is casual religion, but to walk in relationship to the Living God through Jesus Christ requires total commitment. Romans 12:1 says we are to "present ourselves." James 4:7 says "submit yourselves...to God." Presented and submitted into the hands and requirements of God means constant readiness to do His will.
Romans 12:9-21 says, "Let love be genuine. Abhor what is evil; hold fast to what is good. Love one another with brotherly affection. Outdo one another in showing honor. Do not be slothful in zeal, be fervent in spirit, serve the Lord. Rejoice in hope, be patient in tribulation, be constant in prayer. Contribute to the needs of the saints and seek to show hospitality. Bless those who persecute you; bless and do not curse them. Rejoice with those who rejoice, weep with those who weep. Live in harmony with one another. Do not be haughty, but associate with the lowly. Never be wise in your own sight. Repay no one evil for evil, but give thought to do what is honorable in the sight of all. If possible, so far as it depends on you, live peaceably with all. Beloved, never avenge yourselves, but leave it to the wrath of God, for it is written, 'Vengeance is mine, I will repay, says the Lord.' To the contrary, 'if your enemy is hungry, feed him; if he is thirsty, give him something to drink; for by so doing you will heap burning coals on his head.' Do not be overcome by evil, but overcome evil with good." (ESV)
There are many powerful commands in such a short space! "Abhor" and "hold fast" alone are strong statements, and encompass a lifetime of application. There is much to think on here, but what is on my mind is simple: if a person who reads these few words thinks for even one moment there is room to live casually in our relationship to God and casually towards the things of and in the world, they are blind, deaf and dumb.
And, don't think we can dismiss the Bible or its commands / directions on how we ought to live and think. It is God's revelation of His Son, Jesus. It is the directive to how we practice our faith. We ought to hold a high value on His word, for God desires to use His word to make us "complete" and ready for "every good work" (2 Timothy 3:16-17).
Christianity is more than "being nice" and "going to church." It is full of violent discipleship -- take for example: "iron sharpens iron" and "every branch...He prunes" and "tested by fire" and "piercing to the division of soul and spirit" (Proverbs 27:17, John 15:2, 1 Peter 1:7 and Hebrews 4:12). All these show how God is willing to give friction, to cut and burn away and to pierce us in soul operation. These are violent, difficult images of discipleship!
Yes, I am freshly convinced there is no such a thing as casual Christianity. Where there is no passion, there is either spiritual sickness or spiritual lostness. God is extremely passionate about us, and our only proper response is to be extremely passionate about Him.